QSAR modelling of water quality indices of alkylphenol pollutants.

The aim of this study was to determine the degradability of 26 Alkylphenols (APs) by Chemical Oxygen Demand (COD) and/or 5-day Biochemical Oxygen Demand (BOD(5)), and to describe these data from Quantitative Structure-activity Relationships (QSARs). Statistical analysis techniques, such as Multiple Linear Regression (MLR), Principal Component Regression (PCR), Partial Least-Squares (PLS) Regression and Neural Network (NN) were carried out to calibrate and validate four-descriptor QSAR models using two different types of descriptor sets. Stable MLR-QSAR models using Leave-One-Out (LOO) were obtained with high predictability performance: r(2) = 0.924, Q(2)(cv) =0.854 for log (1/BOD) model on 24 APs and r(2) = 0.888, Q(2)(cv) = 0.818 for log (1/COD) on all the studied APs. The MLR models, built with four Dragon descriptors selected by Genetic Algorithm (GA), presented the following performances on 24 APs: r(2) = 0.889, Q(2)(cv) = 0.848 for log (1/BOD(5)) and r(2) = 0.885, Q(2)(cv) = 0.834 for log (1/COD) on 26 compounds. From these results, it is expected that the QSAR models generated could be successfully expanded to predict the biological and chemical activities of structurally diverse AP compounds.

Imaging and nanomedicine for diagnosis and therapy in the central nervous system: report of the eleventh annual Blood-Brain Barrier Disruption Consortium meeting.

The blood-brain barrier (BBB) presents a major obstacle to the treatment of malignant brain tumors and other central nervous system (CNS) diseases. The Eleventh Annual Blood-Brain Barrier Disruption Consortium Meeting was convened to discuss recent advances and future directions in imaging and nanomedicine. Two sessions, one on Cell and Molecular Imaging in the CNS and another on Nanotechnology, Nanobiology, and Nanomedicine, were held March 17-18, 2005, in Portland, Ore. CNS imaging presentations targeted differentiating tumor, neural lesions, and necrosis from healthy brain tissue; methods of delivery of imaging agents across the BBB; and new iron oxide-based nanoparticle contrast agents for MR imaging. Nanobiology presentations covered the development of new nanotechnology and its use in imaging, diagnosis, and therapy in the CNS. Discussions at this meeting stressed the role of biotechnology in the convergence of CNS imaging and nanomedicine and are summarized in this article.

Substituent effects on azo dye oxidation by the FeIII-EDTA-H2O2 system.

The effect of substituents on the oxidation of azo dyes in the FeIII-EDTA-H2O2 system was examined at pH 7. 4-(4'-sulfophenylazo)phenol and 2-(4'-sulfophenylazo)phenol, with methyl, methoxy, and halo substituents on the phenolic ring, were used as model systems. Oxidation of the naphthol dyes Orange I and Orange II were also examined. All of the dyes tested were decolorized in the FeIII-EDTA-H2O2 system, but the degree of decolorization varied over a factor of 10. Dyes substituted with one or two halogens were oxidized to a greater extent than the corresponding methyl- or methoxy-substituted dyes. One explanation for the effect of halogen substituents is that they make the phenolic moieties more acidic, which favors the phenolate anion, which is more readily attacked by *OH. This explanation is supported by the observed correlation between charge density of the phenolate anion and the degree of decolorization. Based on an analysis of products formed from Orange II, a probable mechanism for decolorization of phenolic azo dyes by *OH is proposed. In addition, the optimal levels of H2O2 needed for the process have been examined. It appears that high levels of H2O2 could reduce decolorization by scavenging the *OH.

Mass transport effects on the kinetics of nitrobenzene reduction by iron metal.

To evaluate the importance of external mass transport on the overall rates of contaminant reduction by iron metal (Fe0), we have compared measured rates of surface reaction for nitrobenzene (ArNO2) to estimated rates of external mass transport in a permeable reactive barrier (PRB). The rate of surface reaction was measured at a polished Fe0 rotating disk electrode (RDE) in an electrochemical cell, and the rate of mass transport was estimated from a correlation for mass transport in packed-bed reactors. The kinetics of ArNO2 reduction were studied in pH 8.4 borate buffer at a potential below which an oxide film would form. The cathodic current measured in this system was dependent on the electrode rotation rate, and the measured first-order heterogeneous rate coefficient for surface reaction [krxn = (1.7 +/- 0.2) x 10(-3) cm s-1] was about 10 times faster than the first-order mass transport rate coefficient (kmt approximately 2 x 10(-4) cm s-1) estimated for PRBs. The similarity between rates of surface reaction and mass transport suggest that it may be important to consider mass transport processes in the design of PRBs for contaminants such as nitroaromatics that are highly reactive with Fe0.

Effects of natural organic matter, anthropogenic surfactants, and model quinones on the reduction of contaminants by zero-valent iron.

Recent studies of contaminant reduction by zero-valent iron metal (Fe0) have highlighted the role of iron oxides at the metal-water interface and the effect that sorption has at the oxide-water interface on contaminant reduction kinetics. The results suggest that a variety of organic surface-active substances might enhance or inhibit contaminant degradation, depending on the degree to which they promote solubilization, sorption. and/or reaction. Of particular interest is the effect of natural organic matter (NOM), because of its ubiquitous presence in natural waters and amphiphilic properties; anthropogenic surfactants, because of their use in groundwater remediation; and certain quinones, which represent the redox-active functional groups associated with NOM. In this study, no well-defined effects of these substances were found on the reduction of nitro benzene by Fe0, but the reduction of carbon tetrachloride and trichloroethylene (TCE) was inhibited by NOM. Results with carbon tetrachloride showed that the inhibitory effect of humic acids was greater than fulvic acids, but that several quinonoid NOM model compounds (juglone, lawsone. and anthraquinone disulfonate) increased the rate of reduction by Fe0. Isotherms for adsorption of TCE and NOM onto Fe0 showed evidence of competition for surface sites.